The present invention relates to a method of manufacturing a printed circuit board having circuit patterns shielded with a shield layer.
As an example of a method of manufacturing a printed circuit board, there is known a method of manufacturing a printed circuit board having a shield layer formed on an overlaid insulating layer in order to shield circuit patterns formed on one or two sides of a substrate of the board from electromagnetic noises coming from external instruments or other circuit patterns formed on the board in the same way.
FIG. 2 is an illustration showing such an example. In the figure, a circuit pattern (not shown) is formed by the conventional method on one side of an insulating substrate 1, an insulating layer 2 is adhered to the top surface of the circuit pattern except for a junction land 6, and then an electromagnetic-wave shielding layer 4 is adhered to the insulating layer placed on the top surface of the circuit pattern. The junction land 6 is used for connecting the electromagnetic-wave shielding layer 4 to a grounding circuit.
Conductive ink is adhered by the silk-screen printing method to the electromagnetic-wave shielding layer 4 so as to electrically connect the shielding layer to the junction land 6, which is connected to the grounding circuit. Furthermore, the shielding layer 4 is coated with an overcoat 5.
In a conventional method of adhering a shield layer to the junction land 6, conductive ink is adhered to the shield layer 4 in the process of adhering the shield layer to the junction land 6 connected to the grounding circuit. Prior to this process, to improve the adhesion of the shield layer to the junction land 6, either oxide film is formed on the copper film composing the junction land 6 by heat-treating the copper at a temperature between 140.degree. and 150.degree. C. for 30 to 40 minutes in an oven, or the surface of the junction land 6 is roughened by means of a special polishing method. But such conventional methods suffer from the drawbacks that they require extra labor and special treatments.